A record-breaking ocean rower has said she feels “grief and shame” at the state of Britain’s waterways, as she backed proposals for a Clean Water Authority.

MP Roz Savage urged her party to “go further” on its sewage policy and bid to “remove vulture capital investors and replace (them) with benign sources of investment”.

The Liberal Democrat MP for South Cotswolds holds Guinness World Records for becoming the first woman to row across two and then three oceans solo – the Atlantic, Pacific and Indian – and for the longest ocean row by a solo female between Geraldton, Australia and Mauritius in 2011.

Speaking at her party’s autumn conference in Brighton, Ms Savage supported Tim Farron’s proposal to replace Ofwat with a new body called the Clean Water Authority, which could set legally binding targets to prevent sewage discharges into bathing waters and highly sensitive nature sites by 2030, and “lead the transformation of water companies into public benefit companies”.

The successful motion for the body to take on Environment Agency powers has become Liberal Democrat party policy after a vote.

“Being able to swim safely in our rivers on a warm summer’s day just seems like that should be possible without noticing you’re swimming alongside something really disgusting or fearing that you or your pets are going to get sick as a result,” Ms Savage said.

“We shouldn’t have people’s homes and farmland being flooded with sewage. In my constituency, there’s a poor farmer who has lost cattle because they’ve been in sewage-contaminated fields.

“The Thames rises in my constituency, so I feel a very strong kinship with the River Thames. It’s where I first learned to row and I’ve lived in many different places along the course of the river.”

Asked about why she felt “grief” towards the state of Britain’s waterways, the MP replied: “(Water) has been a very big part of my life and a very character-building part of my life.

“I suppose the grief is a sense that a lot of people who are really passionate about and campaigning on the environment feel on a regular basis, when we look at the destruction of our ecosystems and the loss of biodiversity.”

Ms Savage added she wanted to see developers consider rainwater harvesting schemes because “at the moment, we even waste a lot of clean water” which adds to sewage system pressures, and said: “I think we’re at the point now where we have to admit that the experiment with privatising the water companies has been a complete and utter failure, and has not led to better value for customers.

“In fact, we seem to be paying more and not even getting the most basic services that you would expect from a water company, so the model has not worked and we’re calling for the water companies to be turned into public benefit companies so that all surpluses have to be reinvested into infrastructure in the way that they just haven’t been since privatisation.”

On stage at the Liberal Democrats’ conference, Ms Savage told party activists: “As well as revoking the licence of poorly performing water companies, we also need to strengthen the environmental permitting to significantly reduce permissible pollution.

“Storm overflows are meant to be ‘exceptional’, and by ‘exceptional’, I think of the kind of rain that some of us experienced when we were out door-knocking this spring – it was torrential.”

She said: “At the moment when I think about what is happening to our rivers and waterways, I feel grief and shame. I feel grief for the precious ecosystems like our chalk streams that are being destroyed, and I feel shame that as a country, we are still allowing this to happen.”

Proposing the motion, the party’s environment spokesman Tim Farron said: “We very deliberately claim our position as Britain’s effective opposition, and we present a plan for Britain’s waterways that is radical, ambitious, informed by experts, deliverable and necessary.

“Our 72 seats is a triumph, but most importantly, they are a ticket – a ticket to the big league, an opportunity to show Britain that a better way is possible.

“This policy is a big league policy, a serious and ambitious plan to show that politics can actually fix the problems that blight our lives.”

But campaigner Heather Glass, from London, opposed the motion, which she said “recognises that the current regulatory model is not working but then it proposes more regulation as the solution”.

Ms Glass added: “The Clean Water Authority would be a regulatory juggernaut. It would pull many of its enormous powers away from Government, the Environment Agency and local decision-makers. However competent and well intentioned, should a single centralised technocratic regulator have such control over such an important industry?”

The speaker called for localised catchment partnerships when she said: “Imagine local authorities, farming bodies, anglers, charities, developers, water companies within each river catchment working in partnership, rather than against each other.

“Imagine that partnership having the right powers, the right guidance, the right resources to take long-term decisions on investment needs that reflect local circumstances and local ambitions.”